1. Technical Field
The invention relates to a wafer testing, and particularly relates to methods for testing a special pattern and testing a probe card defect in wafer testing.
2. Related Art
Before a final package test of an integrated circuit (IC), a chip probing (CP) has to be performed on each die in a wafer to filter the dies having defects and decrease a fabrication cost. The CP is to use probes of a probe card to contact the die on the wafer, and transmit test signals to the die through the probes to test a function of the die, and finally determine the quality of each die through a test program, so as to obtain a testing map of the wafer.
In the wafer test process, a test machine probably has a false judgement due to a setting error of the test machine, misuse of the probe card or damage of the probe card, etc., which not only causes a poor yield, but also causes loss of products and waste of testing time. FIG. 1(a) and FIG. 1(b) are diagrams illustrating distribution of bad dies in conventional CP, in which each dot represents a bad die obtained after the CP. A bad die distribution in a wafer testing map of FIG. 1(a) presents a random pattern, and a bad die distribution of FIG. 1(b) has a special CP pattern (i.e. concentrated to an upper left partition of FIG. 1(b)). The special CP pattern is probably caused by the aforementioned various reasons, which is required to be efficiently found from the general random CP patterns, so as to decrease a chance of false judgement of the test machine.
A current wafer testing map relies on engineer's judgement based on experiences to determine whether the special CP pattern exists, so as to early discover the problem and repair the test machine. However, manual determination is usually inefficient and wastes labour cost.